This is an extremely unusual and rare grouping of Hemingray experimental pieces. To the best of my knowledge, all have come from the Hemingray dump. The CD 186.2 "The Nut" is the most common of the group. The others are very rare, and some major CD collectors do not have a full set.

All of these are off clear, but the CD 186 on the left has a medium lemon tint. The photo does not show this well.

A bit of trivia: ALL of these CD 186 series styles are made from the exact two piece mold, with only the dome part redesigned. Each of these pieces has 38: on the front (indicating manufacture in 1940) and mold 18 on the rear.

UPDATE:

Recently a patent covering these styles has been found:

http://reference.insulators.info/patents/detail/?patent=U-2392342

They are known as "Spark Gap" insulators, and we have seen a machine drawing of a CD 186.2 labeled as such.